Influence of Particle Size and Density on Particulate Passage Through Alimentary Tract of Holstein Heifers

Rate of passage and marker recovery responses to variations in particle size and density were evaluated. Twelve Holstein heifers were fed for ad libitum consumption chopped alfalfa hay as the sole dietary ingredient. Heifers were pulse dosed with spheres of specific sizes and densities, and total fecal collections were conducted at 4-h intervals for 7 d. Sphere sizes and densities were .32, .64, 1.27 cm; .91, 1.34, and 2.30 g/ml. Fecal marker recoveries for .32, .64, 1.27-cm sizes and .91, 1.34, 2.30-g/ml densities were 43, 30, 29, 11, 76, and 15%, respectively. Alimentary tract mean retention times of the 1.34 g/ml spheres of .32, .64, and 1.27-cm sizes were 48, 38, and 66 h, respectively. Particle size and density influenced marker recovery and passage estimates. The magnitude of response to alterations in density was greater than that for particle size. Results indicate that particle density and particle size are important factors affecting passage through the alimentary tracts of Holstein heifers.